The sphere is a solid figure very important for us: we live on Earth which is almost a sphere. In a sphere, a circle , is the circle resulting from a section by a plane passing through its center and split into two identical hemispheres (see picture), the circular section obtained has the same diameter the field.
The shortest distance between two points on the surface of a sphere is always the circle arc that connects . Therefore, the circles are chosen to plot routes between cities.
Being accustomed to seeing flat maps, not as it is actually spherical Earth, these routes sometimes surprise us. Take, for example, the path Madrid - Los Angeles.
Sometimes, for reasons of flight availability and supply and demand, there are no direct flights to a given origin and destination. Therefore, we find ourselves in the situation start traveling east when in fact our world city is in the west. Example: when to travel from Madrid to Los Angeles you have to first pass through Amsterdam. However, despite this type of flight that we can scale the eternal journey, if you look inside the plane (on the maps are showing their position during flight), we think that the path that is a little odd . What happens is that the planes seek, wherever possible, the great circle from one point to another.
This is achieved by drawing a curved line and never straight. For example, the straight line distance on the regular flat map of Paris to San Francisco is about 12,500 km; however, the circle would be the line following an airplane is 8,980 miles. As we see the differences are enormous. With this, follow the circle can shorten flight times and also reduce the cost of fuel.
Charts and data : Wikipedia and Microserfs.
